Efficacy and Safety of Treatment With an Anti-M2e Monoclonal Antibody in Experimental Human Influenza

Ramos, Eleanor L.; Mitcham, Jennifer L.; Koller, Teri D.; Bonavia, Aurelio; Usner, Dale W; Balaratnam, Ganesh; Fredlund, Paul; Swiderek, Kristine M.

doi:10.1093/infdis/jiu539

Cited by 113 publications

(109 citation statements)

References 16 publications

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“…In line with this, passive transfer of mouse and human monoclonal antibodies directed against M2e can protect against influenza A virus challenge (11,(18)(19)(20)(21). It has also been reported that treatment of experimentally challenged human volunteers with a human monoclonal antibody directed against M2e reduces viral replication and clinical symptoms (22).…”

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confidence: 77%

Structure of the Extracellular Domain of Matrix Protein 2 of Influenza A Virus in Complex with a Protective Monoclonal Antibody

Cho

Schepens

Seok

et al. 2015

J Virol

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The extracellular domain of influenza A virus matrix protein 2 (M2e) is conserved and is being evaluated as a quasiuniversal influenza A vaccine candidate. We describe the crystal structure at 1.6 Å resolution of M2e in complex with the Fab fragment of an M2e-specific monoclonal antibody that protects against influenza A virus challenge. This antibody binds M2 expressed on the surfaces of cells infected with influenza A virus. Five out of six complementary determining regions interact with M2e, and three highly conserved M2e residues are critical for this interaction. In this complex, M2e adopts a compact U-shaped conformation stabilized in the center by the highly conserved tryptophan residue in M2e. This is the first description of the three-dimensional structure of M2e. IMPORTANCEM2e of influenza A is under investigation as a universal influenza A vaccine, but its three-dimensional structure is unknown. We describe the structure of M2e stabilized with an M2e-specific monoclonal antibody that recognizes natural M2. We found that the conserved tryptophan is positioned in the center of the U-shaped structure of M2e and stabilizes its conformation. The structure also explains why previously reported in vivo escape viruses, selected with a similar monoclonal antibody, carried proline residue substitutions at position 10 in M2. Matrix protein 2 (M2) is a structural protein of influenza A viruses and plays an important role in the virus life cycle. This type III membrane protein of 96 amino acid residues has an N-terminal ectodomain (M2e) of 23 residues, a transmembrane domain of 19 residues, and a cytoplasmic domain of 54 residues (1). M2 is classified as a viroporin. Mutational analysis and crystal and nuclear magnetic resonance (NMR) structural analysis of the M2 transmembrane domain revealed that it is composed of a fourstranded coiled coil and that two conserved amino acid residues (M2-His37 and -Trp41) have a key role in acid-induced proton gating (2-5). Following endocytosis of influenza A virions, the acidic endosomal environment activates the M2 channel so that protons enter the virion interior. The resulting acidification loosens the viral ribonucleoprotein complexes from matrix protein 1 (M1), which facilitates their migration through the membrane fusion pore into the host cell cytoplasm (6, 7). M2 can activate the inflammasome, impairs autophagosome maturation, and was recently shown to recruit parts of the autophagosome machinery to sites of virus budding by a conserved motif in its cytoplasmic domain (8, 9).The sequence of M2e is conserved and therefore has frequently been explored for the development of a universal influenza A vaccine (10-13). Immune protection by M2e-directed vaccines has been documented extensively in experimental animal models, including mice, ferrets, and swine (11-13). In addition, a phase I clinical study showed that M2e-based vaccines are safe and immunogenic in humans (10,14). Seasonal influenza A virus infection induces a poor immune responses to M2e, but this weak re...

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confidence: 77%

Structure of the Extracellular Domain of Matrix Protein 2 of Influenza A Virus in Complex with a Protective Monoclonal Antibody

Cho

Schepens

Seok

et al. 2015

J Virol

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“…Vaccines that elicit antibody responses against conserved surface-exposed antigens, such as the stem region of influenza hemagglutinin or M2e, can protect against multiple influenza virus subtypes (1). A potential clinical benefit of M2e-based vaccines can be inferred from a challenge study in human volunteers, which showed that injection of human monoclonal antibody (MAb) TCN-032 directed against M2e 1 day after inoculation of an H3N2 influenza virus resulted in reduced clinical signs and virus shedding compared to placebo treatment (2).…”

mentioning

confidence: 99%

Crystal Structure of the Conserved Amino Terminus of the Extracellular Domain of Matrix Protein 2 of Influenza A Virus Gripped by an Antibody

Cho

Schepens

Moonens

et al. 2016

J Virol

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c; Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium dWe report the crystal structure of the M2 ectodomain (M2e) in complex with a monoclonal antibody that binds the amino terminus of M2. M2e extends into the antibody binding site to form an N-terminal ␤-turn near the bottom of the paratope. This M2e folding differs significantly from that of M2e in complex with an antibody that binds another part of M2e. This suggests that M2e can adopt at least two conformations that can elicit protective antibodies. Human influenza viruses can escape antibody-mediated immunity by varying the antigenic sites in their surface antigens that are most prone to virus neutralization. Vaccines that elicit antibody responses against conserved surface-exposed antigens, such as the stem region of influenza hemagglutinin or M2e, can protect against multiple influenza virus subtypes (1). A potential clinical benefit of M2e-based vaccines can be inferred from a challenge study in human volunteers, which showed that injection of human monoclonal antibody (MAb) TCN-032 directed against M2e 1 day after inoculation of an H3N2 influenza virus resulted in reduced clinical signs and virus shedding compared to placebo treatment (2).M2e corresponds to the surface exposed amino-terminal part of M2 and is 23 amino acid residues long (3). The first nine amino acid residues of M2 are extremely conserved across all reported influenza A viruses. Human and murine M2e-specific MAbs that recognize different parts of M2e have been described, but how these interact with M2e is largely unknown (4-6). Here, we report the crystal structure of M2e in complex with a Fab fragment from a MAb that binds to the highly conserved N-terminal part of M2.The ethical committee of Ghent University approved this mouse protection study. We isolated MAb148 from a BALB/c mouse that had been immunized with a recombinant tetrameric protein of M2e using conventional hybridoma technology (7). Intraperitoneal injection of 200 g of this IgG1 MAb protected mice against a potentially lethal challenge with an H1N1 virus (Fig. 1A). To identify the epitope of MAb148, we transfected a series of alanine mutants of M2 into HEK293T cells. Transfected cells were subsequently fixed and used in an enzyme-linked immunosorbent assay (ELISA). This analysis revealed that M2 residues Ser2, Leu3, Leu4, and Thr5 are critical for MAb148 binding (Fig. 1B). A similar N-proximal epitope in M2e was reported for human MAb TCN-031 and -032 (8). ELISA analysis using wells coated with M2e peptide variants showed MAb148 binding was indifferent to most of the sequence variation in the M2e segment spanning residues 9 to 20 (Fig. 1C). However, we noted reduced binding to the M2e peptide derived from A/Hong Kong/485/97 (Fig. 1C). Also a shorter M2e peptide (SLLTEVETPIRN) proved less accessible for MAb148 binding (Fig. 1C), though in solution this peptide competed with MAb148 for binding the coating full-length M2e peptide as efficiently as full-length M2e (Fig. 1D), suggesting that reduced re...

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“…To address this question, we compared the outcome of both our 2010 placebo group and the 2008 Retroscreen (Retroscreen Ltd., personal communication) placebo group against those reported for placebo groups in other published studies carried out in 2008 (3), 2009 (9), and 2013 (8). These studies were performed according to the same common standard protocol (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The reported postchallenge clinical outcomes for the placebo group of four reported independent clinical trials (3,(7)(8)(9) and one previously unreported study (Retroscreen Ltd., personal communication) were used for the meta-analysis. The placebo agents used in the studies were different, but all the studies were carried out by the same clinical group (Retroscreen Ltd.) and were conducted according to a common challenge protocol ( Fig.…”

Section: Methodsmentioning

confidence: 99%

Meta-Analysis and Potential Role of Preexisting Heterosubtypic Cellular Immunity Based on Variations in Disease Severity Outcomes for Influenza Live Viral Challenges in Humans

Pleguezuelos

Robinson

Fernández

et al. 2015

Clin Vaccine Immunol

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Influenza live viral challenges in humans are valuable models for testing the efficacy of vaccines and antiviral agents. Volunteers are treated with an investigational agent, and their clinical outcomes postchallenge are compared to those of placebo-treated volunteers. Despite using a common protocol, similar recruitment criteria, and similar doses of the same challenge strain, we noticed differences in disease severity outcomes between the placebo groups from different studies. We investigated whether these differences were significant and, if so, whether any pattern and its possible causes could be identified. We Influenza infection elicits a range of immune responses. One such response is the production of strain-specific neutralizing antibodies that confer immunity against infection by the same strain (1). As a result, a key volunteer exclusion criterion in challenge studies is the detection of preexisting neutralizing antibodies (hemagglutination inhibition [HAI], Ͼ10) to the challenge strain. Another such response is the generation of antiviral cellular immune responses. Despite existing evidence as to their protective role during infection (2-4), preexisting cellular immune responses to the challenge strain are not normally assessed during volunteer recruitment.We have developed a novel vaccine (FLU-v) that elicits broad influenza heterosubtypic cellular responses without inducing any significant antibody response (5-7). In humans, FLU-v was found to be safe and well tolerated and, in a live viral challenge study, to induce a vaccine-specific cellular response whose magnitude correlated with reductions in symptom score and viral shedding (7). No such correlations were seen in the placebo group, but we did notice that both viral shedding and symptom score postchallenge were much lower (50%) in our placebo group than those in the placebo group from a previous study. To establish the significance of these differences, we compared the placebo group outcomes of several other influenza live viral challenge studies. All these studies, although involving different placebo agents, were carried out by the same clinical group (Retroscreen Ltd.), using the same recruitment criteria, viral strain and dose, and method for determining postchallenge clinical and virological outcomes. This meta-analysis revealed an "experiment of nature" that we believe provides interesting insights in the potential of the cellular immune system for controlling influenza virus infection. MATERIALS AND METHODSClinical trial data used for meta-analysis. The reported postchallenge clinical outcomes for the placebo group of four reported independent clinical trials (3, 7-9) and one previously unreported study (Retroscreen Ltd., personal communication) were used for the meta-analysis. The placebo agents used in the studies were different, but all the studies were carried out by the same clinical group (Retroscreen Ltd.) and were conducted according to a common challenge protocol (Fig. 1) that used the same well-defined recruitment criteria, vi...

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Efficacy and Safety of Treatment With an Anti-M2e Monoclonal Antibody in Experimental Human Influenza

Cited by 113 publications

References 16 publications

Structure of the Extracellular Domain of Matrix Protein 2 of Influenza A Virus in Complex with a Protective Monoclonal Antibody

Structure of the Extracellular Domain of Matrix Protein 2 of Influenza A Virus in Complex with a Protective Monoclonal Antibody

Crystal Structure of the Conserved Amino Terminus of the Extracellular Domain of Matrix Protein 2 of Influenza A Virus Gripped by an Antibody

Meta-Analysis and Potential Role of Preexisting Heterosubtypic Cellular Immunity Based on Variations in Disease Severity Outcomes for Influenza Live Viral Challenges in Humans

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